Combination locks are used in a variety of applications, including, for example, with enclosures such as lockers, storage sheds, and various gates and doors. The locking mechanism of a conventional single dial combination lock 1 is schematically illustrated in FIG. 1. A numbered combination dial 2, which serves as the user interface, is positioned on an external surface of the lock 1. Rotation of the dial causes a drive plate 3 to engage a series of rotating tumbler disc 4a, 4b, 4c (usually three for a conventional combination padlock or school locker lock), each having an outer periphery which holds a lever or fence 7 in a locking condition. Detents or lugs 9 extending from each of the tumbler discs 4a, 4b, 4c engage each other to cause the tumbler discs 4a, 4b, 4c to rotate together. The innermost tumbler disc 4a may, but need not, be rotationally fixed to the drive plate 3.
When the dial 2 is rotated to a first desired rotational position and then rotated in an opposite direction (for example, the counterclockwise direction), the outermost or third tumbler disc 4c remains in a desired rotational position due to separation from the detent 9 of the middle or second tumbler disc 4b. When the dial is then rotated to a second desired rotational position and then rotated in an opposite direction (for example, the clockwise direction), the second tumbler disc 4b remains in a desired rotational position due to separation from the detent 9 of the innermost or first tumbler disc 4a. When the dial 2 is then rotated to a third desired rotational position, the first tumbler disc 4a is positioned accordingly. In this fashion, the dial 2 may be rotated to successive desired positions (identifiable by alignment numbers on the dial 2, with a detent, notch, or other indicator on the lock housing) that align notches 6 in each of the tumbler discs 4a, 4b, 4c with the lever 7.
When all of the notches 6 are aligned with the lever 7, the lever may be permitted to move into the aligned notches 6 (for example, by user movement or by a spring loaded mechanism). In one embodiment, this lever movement may allow a locking member 5 to move out of locking engagement with a locked obstruction, such as, for example, a shackle, to allow withdrawal of the shackle. In another embodiment, engagement of the lever 7 with the aligned notches 6 may allow lateral movement of the lever 7 and a connected locking member 5 (e.g., a slideable locking bolt) by continued rotation of the combination dial 2 and the engaged tumbler discs 4a, 4b, 4c beyond the third successive desired rotational position, for retraction of the locking bolt to disengage a corresponding locking component (e.g., a locker frame or an interengaging latch).
While the use of a combination lock, as compared to a key based lock, may eliminate the risk of lost, stolen, or copied keys, an authorized combination may still be learned by an unauthorized user, or known by a once-authorized user to whom access is no longer desired (e.g., when a locker is assigned to a different student in a subsequent school year). In these and other circumstances, an authorized user or administrator may wish to change the unlocking combination. In a conventional combination lock, the authorized combination code may be changed to one of several optional combination codes by axially separating the drive plate from the first, innermost tumbler disc, such that the rotational position of the dial and drive plate with respect to the first tumbler disc may be adjusted. This results in a change in the numerical permutations of the authorized combination code.